1. Field of the Invention
The present invention relates to a cleaning blade, a method for manufacturing the cleaning blade, and a process cartridge and an electrophotographic apparatus each including the cleaning blade.
2. Description of the Related Art
In general, even after a toner image formed on a surface (outer peripheral surface) of an electrophotographic photosensitive member (hereinafter also referred to simply as a “photosensitive member”) is transferred to a transfer medium or an intermediate transfer member or even after the toner image is further transferred from the intermediate transfer member to a transfer medium, a portion of toner tends to remain on the photosensitive member and/or the intermediate transfer member. Thus, residual toner on the photosensitive member or the intermediate transfer member must be removed, for example, with a cleaning blade. An existing cleaning blade may be of a plate-like shape and may have a thickness of 1 mm or more and 3 mm or less. The longitudinal length of a face of the existing cleaning blade opposite a member to be cleaned (such as a photosensitive member or an intermediate transfer member) may be greater than the thickness.
A cleaning blade may be fixed to a metallic holder in an electrophotographic apparatus such that an edge (front ridgeline) of the cleaning blade comes into contact with a member to be cleaned.
Urethane rubber is commonly used in cleaning blades because of its high wear resistance and resistance to permanent deformation.
One known toner that has been developed to meet the recent demand for high image quality has a small particle size and a high degree of sphericity (close to spherical). This toner having a small particle size and a high degree of sphericity advantageously has relatively high transfer efficiency and can meet the demand for high image quality.
However, it is difficult to properly remove such a toner having a small particle size and a high degree of sphericity with a cleaning blade from the surface of a member to be cleaned, thus often resulting in faulty cleaning. This is because a toner having a small particle size and a high degree of sphericity more easily slips between the cleaning blade and the member to be cleaned than other toners.
It is effective to increase the contact pressure and reduce the gap between a cleaning blade and a member to be cleaned to prevent the passing of toner.
However, a higher contact pressure between a cleaning blade and a member to be cleaned tends to result in a higher friction force between the cleaning blade and the member to be cleaned. A higher friction force between the cleaning blade and the member to be cleaned increases the likelihood that the cleaning blade is drawn in the movement direction of the surface of the member to be cleaned and the edge of the cleaning blade catches on the surface of the member to be cleaned (turning over). The cleaning blade may make an abnormal noise when the cleaning blade returns to its original position against the drawing force. Continuous cleaning with a cleaning blade having a turned-over edge tends to cause local wear in the vicinity of the edge of the cleaning blade (several to several tens of micrometers separated from the edge). Further continuous cleaning increases the local wear, and consequently toner cannot be properly removed.
From the perspective of extended-life of a cleaning blade and a member to be cleaned and energy conservation, it is necessary to reduce the rotation torque of the member to be cleaned during cleaning (torque reduction). For torque reduction, it is effective to reduce the friction on the surface of a portion of a cleaning blade in contact with a member to be cleaned.
Regarding torque reduction, Japanese Patent Laid-Open No. 2008-268670 discloses a technique for including fine particles having an average particle diameter of 3 μm or less in a surface layer of a urethane rubber (urethane elastomer) cleaning blade that comes into contact with a member to be cleaned.
Japanese Patent Laid-Open No. 2012-150203 discloses a technique for providing a contact portion of a cleaning blade that comes into contact with a member to be cleaned with a surface layer having higher hardness than a base layer of the cleaning blade.
Japanese Patent Laid-Open No. 2009-025451 discloses a technique for continuously increasing the nitrogen concentration of a contact portion of a cleaning blade that comes into contact with a member to be cleaned from the interior to the surface of the contact portion.
Japanese Patent Laid-Open No. 2001-075451 discloses a technique for increasing the isocyanurate group concentration on the surface of an edge of a urethane rubber (urethane elastomer) cleaning blade as compared with the isocyanurate group concentration of the interior of the edge.
However, studies of the present inventors showed that these techniques of the related art have the following problems.
In such a two-layer cleaning blade having a surface layer and a base layer as described in Japanese Patent Laid-Open Nos. 2008-268670 and 2012-150203, the surface layer and the base layer behave differently when the cleaning blade is in contact with a member to be cleaned. Thus, the surface layer sometimes peeled off or chipped because of concavities and convexities (typically 1 μm or more and 2 μm or less) or foreign substances (including toner) on the surface of a member to be cleaned. In the technique described in Japanese Patent Laid-Open No. 2008-268670, it is difficult to uniformly disperse the fine particles in the surface layer. Nonuniform dispersion of the fine particles sometimes caused variations in characteristics in a contact portion, local chipping, or faulty cleaning.
The technique described in Japanese Patent Laid-Open No. 2009-025451 increases the cross-linking concentration on the surface of a contact portion of a urethane rubber (urethane elastomer) cleaning blade that comes into contact with a member to be cleaned to form a hard segment. However, the technique sometimes insufficiently reduced the torque.
The technique described in Japanese Patent Laid-Open No. 2001-075451 involves applying a liquid mixture of an isocyanate compound and an isocyanurating catalyst to an inner surface of a die to increase the isocyanurate group concentration on the surface of a urethane rubber (urethane elastomer) cleaning blade. An increase in the isocyanurate group concentration to achieve substantially constant hardness and a sufficient torque reduction in the vicinity of the surface of the cleaning blade sometimes resulted in poor adaptability to concavities and convexities or foreign substances on the surface of a member to be cleaned. Poor adaptability to concavities and convexities or foreign substances on the surface of a member to be cleaned tends to result in the passing of toner.
In these techniques of the related art, a cleaning blade often has insufficient adaptability to toner particles or particles having the size of toner particles between the cleaning blade and a member to be cleaned. More specifically, a contact portion of a cleaning blade that comes into contact with a member to be cleaned sometimes changed its shape at a very large curvature radius on a particle between the cleaning blade and the member to be cleaned. Thus, toner particles around the particle sometimes passed between the cleaning blade and the member to be cleaned.